Factors influencing the use of postoperative bilevel positive airway pressure (BiPAP) in patients undergoing adult cardiac surgery: A retrospective cohort study

Abstract BAckground and Aims Respiratory complications are one of the biggest challenges following cardiac surgery, which can lead to hypoxia and acute respiratory failure (ARF). The aim of this study to identify the factors led to BiPAP application for postoperative respiratory complications and its effectiveness as the main outcome measures after cardiac surgery. Methods It was a retrospective cohort study with consecutive sampling technique. A total of 335 postcardiac surgery patients medical record was reviewed who were underwent for surgery from November 1, 2018 to November 30, 2019. 265 patients were finalized for the recruitment, five patients were excluded before the final analysis. Data of 260 patients were analyzed for compiling of results. Results The mean age was 59 years. 196 (75.4%) patients were males and females were 64 (24.6%). Mean weight was 72 kg and mean body mass index (BMI) 26.67 kg/m2 . BiPAP application was in 38 (14.6%) patients and significantly high in with high BMI, (p < 0.05). There are significant associations of BiPAP application patients with COPD (p < 0.05). Patients with positive fluid balance, cardiac dysfunction, and required inotropic support were significantly associated with BiPAP need (p < 0.05), respectively. Conclusion BiPAP is effective to treat ARF and other respiratory complications after adult cardiac surgeries. High BMI, atelectasis, and pneumonia are also the independent factors causing ARF. BiPAP can be a successful tool for preventing the adverse effects of postoperative pulmonary complications after cardiac surgery.


| INTRODUCTION
Postcardiac surgeries pulmonary problems are always matter of worries for both cardiac surgeons and anesthesiologists. These complications could have variety of mild respiratory impairment to acute respiratory distress syndrome (ARDS). Atelectasis is one of the known primary trigger of many complications, and further may lead to hypoxemia and pneumonia. Respectively one of these issues raises the risk of morbidity and mortality. 1 Postoperative risk of respiratory complications is increased by anesthesia, pain of sternotomy cardiopulmonary bypass, thoracotomy, diaphragm malfunction, fluid overload, major transfusions, and the patient's pre-existing condition. These problems are linked to a longer stay in the hospital and a lower chance of recovery. 2 Despite advances in perioperative care, after cardiac surgery respiratory failure remains a common complication after cardiopulmonary bypass (CPB). It further leads to mortality and morbidity.
To minimize pulmonary function impairment, various techniques have been developed, including perioperative mechanical ventilation (MV), restrictive transfusion, technological modifications of CPB, and drug administration, such as steroids and aprotinin. 3,4 Application of noninvasive ventilation (NIV) like BiPAP, using face or nose masks has reduced the necessity of endotracheal intubation. It has been recognized that BiPAP can prevent atelectasis and postoperative pneumonia, it also has beneficial effects in postoperative phase of cardiac surgery to prevent other pulmonary complications.
The main purpose of this study to see the factors led to BiPAP application for postoperative respiratory complications and observed its effectiveness as main outcome measures in patients after cardiac surgery.

| Objectives
The main objectives of this study to see the factors led to BiPAP application and its effectiveness to manage postoperative respiratory complications as main outcome measures in patients after cardiac surgery.

| Design
It was retrospective cohort study with consecutive sampling technique. The consent was not required as there was no direct involvement and questioning to patients. General and thoracic surgery patients were excluded. All data were collected from patient's medical record. Total of 335 patients' medical record was reviewed who were undergone for cardiac surgery. 70 patients' data were not considered due to missing information.

| Settings
As it was a retrospective cohort study, therefore it was exempted by

| Participants
All records of the patients with either gender scheduled for cardiac surgery at cardiac operating rooms, then shifted in coronary care unit (CICU) after surgery were included.

| Main outcomes measures
The main outcome measures of this study to identify the factors led to BiPAP application and its effectiveness for postoperative respiratory complications in patients after cardiac surgery.

| Statistical analysis
All statistical analyses were carried out using version 21 of the statistical packages for social science (SPSS Inc.). Median and 25th-75th percentile was computed for quantitative variables and analyzed by Mann-Whitney U test. Whereas qualitative variables were reported in term of frequency and percentage and analyzed by Chi-square or Fisher's exact test. For the two-sided tests, p-value < 0.05 was considered the significant threshold.

| RESULTS
Overall documentation compliance was found 79.10%. In demographic data (Table 1) Table 2. There are significant association of BiPAP need with chronic obstructive pulmonary disease (COPD) where (p < 0.05), details of other co-morbids are given in Table 3.
Additionally, postoperative application of BiPAP was high in patients who were already intubated and operated on emergency basis.
We have observed some intraoperative variables that could effect on outcome in terms of postoperative BiPAP need.
We have found that patients with positive fluid balance, and patients with cardiac dysfunction requiring inotropes were significantly associated with respiratory complications and BiPAP application. There is p-values <0.05 respectively shown in Table 4.
We have also monitored triggers and clinical conditions which have leads to BiPAP application postoperatively are shown in Table 5. Respiratory dysfunction, varies from minor to major, is a known side effect of cardiac surgery. The length of cardiopulmonary by-pass, dysfunction of diaphragm, major transfusion, postoperative pain, fluid overload, and the patient's pre-existing comorbidities all lead to the jeopardy of respiratory complications following surgery. [5][6][7][8][9][10][11] BiPAP as a part of noninvasive ventilation (NIV), has been evaluated in after cardiac surgery to prevent acute respiratory failure ARF. 12 The severity of these surgical complications might extent from minor pulmonary ailment to acute respiratory distress syndrome (ARDS). 13,14 Atelectasis is one of the frequent pulmonary complications that can develop following cardiothoracic surgery. The effect of general anesthesia, cardiopulmonary bypass (CPB), gas exchange impairment during surgery, and ceasing lung perfusion, are the major causes of atelectasis. 15 Each of these complications increases the incidence of morbidity and mortality.
BiPAP as a noninvasive ventilation approach has minimized the need for endotracheal intubation. Several studies have recently shown that BiPAP can improve hypoxemia and reduce atelectasis in patients after extubation following to cardiac surgery. [16][17][18][19][20] Obese cardiac surgery patients have higher rates of hypoxemia, atelectasis, and respiratory dysfunction, and short-term use of BiPAP improved pulmonary function and reduced the need for reintubation. 21 In our study we have found that increase in BMI is strongly associated with need of application of BiPAP after cardiac surgery. It also showed improvement in respiratory parameters after application of BiPAP in obese patients. A study by Lin 25   especially in those patients in those patients in whom PaO 2 was less than 60 mmHg.
We have also looked patients for the need of BiPAP with or without inotropic support and found that patients who required inotropic support significantly required mechanical ventilation, and BiPAP were applied for breathing support. That finding supports existing literature, that inotropic support to help in weaning the patients from mechanical ventilation.

CONFLICTS OF INTEREST
The authors declare no conflicts of interest.

DATA AVAILABILITY STATEMENT
The data that support the findings of this study are available on request from the corresponding author. The data are not publicly available due to privacy or ethical restrictions.

ETHICS STATEMENT
Participant consent is not applicable as the data was required from Patient Medical record. Whereas the study got exemption from Ethical Review Committee of Aga Khan University Hospital. All methods were performed in accordance with the relevant guidelines and regulations. The consent was obtained for all patient record, personally identifiable data.

TRANSPARENCY STATEMENT
The lead author Khalid Maudood Siddiqui affirms that this manuscript is an honest, accurate, and transparent account of the study being reported; that no important aspects of the study have been omitted; and that any discrepancies from the study as planned (and, if relevant, registered) have been explained.